1. Field of the Invention
The present invention relates to a copying machine for copying a document through the steps of feeding out a plurality of stacked document sheets one by one, arranging two document sheets on a glass platen in series with respect to a document conveying direction, and copying images of the two document sheets onto one large-size sheet.
2. Description of the Prior Art
Conventionally, as a copying method using an electrophotographic method, from copy-saving and filing-space-saving points of view, a two-in-one mode copying method (hereinafter, referred to as "two-in-one mode") has been known by a Japanese Patent Laid-Open Publication No. 3-114071, a Japanese Patent Publication No. 5-73095, and the like. In this two-in-one mode, document sheets placed on a document tray of an automatic document feeder (ADF) are fed onto the glass platen one by one. On the glass platen, the document sheets are set in such a way that two sheets at each one time are arranged in series with respect to the document conveying direction and that one end of one document sheet is made coincident with an exposure reference (for example, one side line of a scale provided upstream or downstream of the glass platen in the document conveying direction) while one end of the other sheet is made coincident with the other end of the one document sheet. Then, the two document sheets are exposed to light by a single scanning Operation. As a result, the two document sheets are copied onto a copying sheet of the same size as the original document sheet. More specifically, if the document sheets are of A4 size transverse, then the two document sheets are copied onto a sheet of A4 size longitudinal in reduction at a magnification factor of 0.707.
In the two-in-one mode as described above, it is important to arrange the two document sheets with their ends coincident with each other at the exposure position on the glass platen irrespectively of the quality of the document, and to make one end of the first document sheet accurately coincident with the exposure reference.
Two ways may be available for solving the above problem. A first way is to give such a feed amount that two document sheets reach the exposure position, with the rear end of the first document sheet coincident with the front end of the second document sheet, whereby the two document sheets are stopped in the exposure position. A second way is to convey the document sheets with a gap provided between the first and the second document sheets, and bringing the front end of one document sheet positioned on the side close to the scale into contact with the scale, whereby the one document sheet is moved relative to the other document sheet so that the interval between the document sheets is lessened.
However, in the second way including the step of bringing the document sheet into contact with the scale, if the document sheet is thin paper having a low bending strength or paper having a very high coefficient of friction, the document sheet may be bent when brought into contact with the scale, which in turn may incur paper jam, as possible problems. Therefore, although the second way has an advantage that the document sheets can be arranged more accurately to the exposure reference, the first way would be preferred to the second way when thin document sheets or the like are used. Also, the interval between one document sheet and another to be set in the second way should be controlled to a proper value depending on the quality (strength) of the paper used or the like.
In the two-in-one mode, in view of the bookbinding state of copied sheets, it is necessary to copy the image of a document sheet having the smaller page number out of the two sheets of document onto the left half of a sheet and to copy the original image having the larger page number onto the right half of the sheet. Therefore, when the two-in-one mode is executed with a copying machine which consists of a copying machine main body having an exposure reference at the left end of the glass platen as viewed from the operator side and an automatic document feeder for feeding stacked document sheets in order of decreasing page number of the document sheets and for conveying a document sheet in a direction from right to left side on the glass platen, it has been arranged that one end of the document sheet having a larger page number is made coincident with the exposure reference.
According to the above-described copying machine, when the number of document sheets stacked on the document tray is an even number, all the document sheets are copied in such a way that the image of one document sheet having a smaller page number is copied onto the left side of a sheet and the image of another document sheet having a larger page number is copied onto the right side of the sheet. However, when the number of document sheets stacked on the document tray is an odd number, the first-page document sheet to be set last would be copied with its one half blank. For prevention of this, even if the last-page document sheet is first set in one sheet alone previously, its one end is made coincident with the exposure reference so that only the last-page document would be copied onto an opposite side, i.e., the right side on a sheet, as a problem. This problem could be solved by such a measure that the last-page document sheet is positioned with its top on the operator side, i.e., upside down, or that the document sheet is conveyed from left to right side. Unfortunately, it would be unreasonable to expect such an operation on users.
Some automatic document feeders are arranged to feed document sheets stacked on the document tray by starting with its first page or with its last page. Also, other automatic document feeders are arranged to feed document sheets in a direction from left to right side on the glass platen. Meanwhile, some copying machines have the exposure reference position on the left side of the glass platen, and ethers on the right side.